Transcript The Sea Floor

The Sea Floor
CH 2 pg 19
Geosphere
• Geological processes influenced terrestrial and
marine environments
• Earth is broken into layers..
– Crust
– Mantle
– Core (inner/outer)
Geological Layers of Earth
• Crust - 1% Earth’s mass thinnest layer
–Continental
»Granite, less dense, floats on top
oceanic
– Oceanic
»Basalt, dense, thinner than continental
Lithosphere is part of the upper mantle
• Mantle - layers beneath the crust
–Lithosphere (broken into plates; tectonic)
–Asthenosphere (plates float on top)
»“Silly putty”
»Heated and becomes less dense so
material rises then as it cools material
sinks creating circulating currents called
convection currents
»Causes plates to move
Geological Layers of Earth
• Core - innermost layer
–Outer core
»Dense liquid
»Moves counter clockwise thought to
create magnetic field
–Inner core
»Solid due to pressure
»Iron and Nickel
Oceans
• 71% of Planet
• Regulate climate and atmosphere
Geography of the Ocean Basin
• 2/3 of the earth’s land area in the Northern
Hemisphere
• The Southern Hemisphere
– 80% of the ocean
Five Large Basins
• Pacific Ocean
• deepest (approx. 14000 ft) and the largest
• narrowing
• Atlantic Ocean
• Slowly getting bigger
• Indian Ocean
• Arctic Ocean
• Southern Ocean
• Difference between ocean and sea?
The Origin and Structure of the Ocean Basins
• (1912) Continental Drift Theory
– All the continents had once been joined in a
single “supercontinent” called Pangea
– Approx 180 m.y.a.
• (1950s and 1960s) Plate tectonics
– Plates did drift lead to the discovery of the
Mid-Ocean Ridge
Evidence
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Pieces of a puzzle
Matching sequences of rock & mountains
Distribution of organisms
Magnetic fields
– Igneous rock
– Magnetite and iron
• The Mid-Ocean Ridge
– System of volcanic mounts that encircles the globe
– Largest geological feature on earth
– Submarine mountains can break the surface of the water
to form islands (ex. Iceland)
– Eastern – Pacific Ridge (Subduction)
Subduction vs Divergent
Creation of the Sea Floor
• Pieces of oceanic crust separate mid-ocean
ridges by creating cracks called rifts.
– Rifts release the pressure on the mantle
– Reduced pressure allows hot mantle material to rise
up through the rift.
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The magma pushes up around the rift
It cools as it enters the surrounding water
Creating a ridge
Atlantic Ocean getting larger (Divergent)
Creating New Seafloor
• Repeating process makes the seafloor
move away from the mid-ocean ridge
• Mid-ocean ridge form the edges of
continents
• As the plates move the continent is carried
with it (2.5 ~ 7cm/year)
• Seafloor younger closest to the ridge
Aleutian Islands pg 28
•Trenches curve due to Earth’s spherical
shape
•Volcanic islands follow trenches
•Island Arcs
Hot Spots pg 36
• Hawaiian Islands (plate movement) vs
Aleutian Islands (subduction)
• Hawaiian Islands are formed as a result of
the movement of plate over a “hot spot”
– Magma oozes from the thinner oceanic crust
– Cools and creates a seamount
– Eventually breaks the surface
– Southern islands are younger
Continental Volcanoes pg23
• Collision between ocean and continental
plates result in volcanoes
• Continent vs Continent
– Himilayas & Great Smokey Mountains
Transform Boundaries
• Shear boundary
– Plates that slide past each other
– Friction prevents the plates from sliding
smoothly
– They lock up and stress builds up until the
plates break free
– Cause an earthquake
– San Andres Fault (pg 29)
The Ocean Floor
• Sea floor is dominated by plate tectonics
• Sea floor is divided into two main regions;
– Continental margin
– Deep-sea floor
Continental Margins
• Region between the continental crust and
oceanic crust
– Continental Shelf
– Continental Slope
– Continental Rise
Continental Shelf
• Shallow makes up 8% of
the ocean’s surface area
• 400-600 ft deep
• Rich in life ends at the
shelf break
• Continental crust
covered in sea water
Continental Slope
• Exact edge of the continent
• Starts at the shelf break
• Descends to the deep-sea
Continental Rise
• Sediment forms at the base of the
continental slope
• Deep-Ocean Basins
– 10,000 – 16,500 ft deep
– abyssal plain
• Mariana Trench
– West Pacific
– Depth of 36,163ft (7 miles)
Hydrothermal Vents
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Fractures in crust water seeps down
Heated water pushes its way up
Creating a hydrothermal vent
Temp ranging from (50 – 550o)
The water contains minerals and sulfides
• As the water cools the minerals solidify
and deposit themselves around the vents
creating chimneys, commonly called black
smokers.
• Tallest chimney so far rises 200 ft above
sea floor